<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button>显示当前时间</button>
    <div>某个时间</div>
    <p></p>
    <script>
        var btn = document.querySelector("button");
        var div = document.querySelector("div");
        btn.onclick = function() {
            div.innerText = getDate();
        }
        var p = document.querySelector("p");
        p.innerText = getDate();

        function getDate() {
            var date = new Date();
            var year = date.getFullYear();
            var month = date.getMonth();
            var day = date.getDate();
            var days = date.getDay();
            var arr = ["星期天", "星期一", "星期二", "星期三", "星期四", "星期五", "星期六"]
            return "今天是" + year + "年" + month + "月" + day + "日" + arr[days]
        }
    </script>
</body>

</html>